1. Field of the Invention
The present invention relates to a cleaning system of a steam generator and, more particularly, to a cleaning system which is capable of cleaning the heat transfer tubes and a plurality of tube support plates supporting the heat transfer tubes, which are installed to the inside of a steam generator, using a cleaning device transferred along a guide rail installed to an upper hand hole of the steam generator, in which the cleaning device is installed to an ascending/descending means which is vertically transferable, such that the plurality of tube support plates and the upper bundle of the heat transfer tubes can be cleaned.
2. Description of the Related Art
The steam generators, specially which are Westinghouse F-Models, are presently installed in Gori nuclear power plant, Units 2, 3, and 4 and Young Gwang nuclear power plant, Units 1 and 2, in the Republic of Korea. The steam generator serves to generate steam to drive a turbine generator by heat exchange. More specifically, as radioactive water containing heat energy generated in a reactor flows in thousands of heat transfer tubes in a high temperature and high pressure state, and transfers its heat energy to the non-radioactive water flowing outside the heat transfer tubes, the non-radioactive water is changed into steam.
On the other hand, when the steam generator is operated in a state where the heat transfer tubes are damaged, the radioactive water flowing in the heat transfer tubes leaks and mixes with the non-radioactive water. Then, the steam converted from the non-radioactive water contaminated by the radioactive water causes radioactive pollution in the steam receiving areas. Because of this, it is important to secure the integrity of the heat transfer tubes so as not to cause such radioactive pollution.
The steam generator is configured such that: thousands of heat transfer tubes, which are U shaped, i.e., U-tubes, are formed as a bundle, which is called a tube bundle; both ends of each U-tube are fixed to a tube sheet located at the lowest part of the tube bundle; and the heat transfer tubes are supported by tube support plates at seven stages which are spaced every about 1 m from the bottom to the top. However, the conventional steam generator is disadvantageous because impurities are inputted from various paths while operation soft water passes through the paths or generated therein. These impurities can change into scales on the outer surfaces of the heat transfer tubes causing the heat exchange efficiency to be decreased. Also, when scales are deposited between the heat transfer tubes and the tube support plates become a sludge that gradually solidifies, denting occurs between the tube support plates and the heat transfer tubes that damages the heat transfer tubes. Therefore, removal of the scales and the sludge is necessary to secure the efficiency of the steam generator and the integrity of the heat transfer tubes.
However, the conventional systems installed in the nuclear power plants are cleaned by a cleaning device inserted though a hand hole in the steam generator that just removes sludge on the tube sheet, to which the heat transfer tubes are fixed.
Therefore, it is necessary to clean the plurality of tube support plates and the heat transfer tubes of the upper bundle.